Many commercial products use a lead-acid or other battery for backup operation applications. These products require circuits to recharge their backup batteries. The heretofore known constant-voltage lead-acid battery chargers include circuits based on adjustable linear regulators, and circuits based around single-chip charger I.C.'s. Those configured around adjustable linear regulators had few components but required manual adjustment of a potentiometer to set the charge voltage to within the required tolerance (about .+-.1%). This required costly time and labor during manufacturing. Such circuits also typically made no provision for limiting the maximum amount of current delivered to the battery, which forced the circuit's power supply to be more robust than desired, leading to extra cost, or forced the circuits to endure overloading when highly-discharged batteries were first attached to the charger.
The circuits based around single-chip charger I.C.'s, such as the Unitrode UC3906, required many support components around the I.C., such as resistive voltage dividers and series-pass transistors, and bore the additional cost and single-sourcing problems of the charger I.C.'s themselves.